An automatic voltage regulator using a toroidal autotransformer can be implemented using various regulator windings. However, the output voltage of such a regulator is always determined by the winding of its primary and secondary coils. Thus, in order to output various voltages, an automatic voltage regulator using a toroidal autotransformer is designed to wind coils according to the desired voltage or have several output taps.
For example, as illustrated in FIG. 1, an autotransformer can be designed to have a plurality of taps (a, b, c) on a field winding (200) excited in a main winding (100) so as to output various voltage levels. If the toroidal autotransformer is so designed that in case where 220V is applied to the main winding (100), 20V is applied to both ends of the main winding (100) and each tap of the field winding (200) reduces the voltage by 5V, the toroidal autotransformer can supply 200V from the first tap (a), 205V from the second tap (b), and 210V from the third tap (a), to an output terminal.
As such, conventional automatic voltage regulators supply discrete output voltages with a large deviation between the voltages. For example, in the example as described above, each of the output voltages with a deviation of 5V, i.e., each of 200V, 205V and 210V, is selectively supplied. Accordingly, conventional automatic voltage regulators cannot provide precise voltage control.
As such, conventional automatic voltage regulators, providing low precision, are very inconvenient for users. We will explain this in more detail with an example of a power saving device using an automatic voltage regulator providing low precision.
In the case of a high-story apartment, a distribution board is installed in a basement. About 235V is supplied to the first floor, but the supply voltage decrease as the floor gets higher, and as a result, about 205V is supplied to the 15th floor. In general, an electronic appliance can operate in a stable manner when a voltage of 205V is supplied. Thus, in case where each house uses a power saving device which decreases the voltage by about 10V, it is not ensured that a house supplied with a voltage of 215V or lower will obtain at least the minimum voltage required for providing stable operation, 205V, due to the use of an inappropriate power saving device. Meanwhile, in the case of the highest floor, it is necessary to increase the voltage level so that a stable voltage can be supplied in a consistent manner.
That is, in the case of a high-story apartment, there is a large deviation in the system voltage provided to a consumer between low floors and high floors. The floors of a high-story apartment are classified into floors where the voltage needs to be reduced to save power and floors where the voltage needs to be increased so that a stable voltage can be supplied. However, conventional automatic voltage regulators are not capable of supplying voltage levels with such a large deviation between them while controlling the voltages precisely, and accordingly users have suffered great inconvenience.
The present invention solves the problems of conventional technology; the present invention provides an automatic voltage regulator capable of precisely controlling the voltage level and thereby of supplying an appropriate voltage.
Meanwhile, in order for a conventional automatic voltage regulator to operate in a power electronic system, complex features such as a main transformer, excitation transformer, detection transformer, highly sensitive effective value detection circuit, high speed A/D transform circuit, triac switching circuit, etc. are required. As a result, conventional automatic voltage regulators have such high prices that they are used in a special case such as an experiment requiring expensive laboratory equipments. Thus, a general user cannot afford such regulators, and thus the conventional regulators do not have marketability.
In addition, because such complex devices cannot operate normally if the frequency and level of a system voltage changes, conventional automatic voltage regulators have to be manufactured in consideration of electricity environment.
In contrast, the automatic voltage regulator of the present invention has a simple structure which does not use a power semiconductor circuit, and thus can control voltage precisely regardless of electricity environment.
Meanwhile, the reason why conventional automatic voltage regulators selectively output discrete output voltage levels with a large deviation between them is because the regulators output an output voltage from a tap fixedly placed on a secondary coil.
The reason for the technical limitation is because a very limited range of winding methods have been used for a toroidal core. In the current process of producing a toroidal core, a main winding is wound on a toroidal core, and then a coil of a certain thickness is wound on the main winding to form field windings where input/output taps are formed. If a non-conductive coil is inserted between the main winding and field windings of a toroidal core, problems occur such as generation of fumes from the inserted coil. Thus, in this process, only field windings serially connected by taps and a main winding are used.
The present invention is to improve such a winding method for conventional toroidal cores and thereby to output various levels of inductive voltages.